A well-known problem in electronic devices is that of heat dissipation. High temperatures often limit the performance and/or lifetime of such devices. This is a particular problem in semiconductor devices which operate at high power and/or high frequency such as microwave amplifiers, power switches and optoelectronic devices. It is therefore desirable to be able to spread any heat generated by component devices to reduce temperatures and thus improve device performance, increase lifetime, and/or increase power density. Accordingly, it is desirable to utilize a heat spreading substrate material with a high thermal conductivity to spread the heat generated by electronic device components, lowering the power density and facilitating dissipation via a heat sink thus improving device performance, increasing lifetime, and/or enabling an increase in power density.
Diamond has unique properties as a heat spreading material, combining the highest room temperature thermal conductivity of any material, with high electrical resistivity and low dielectric loss when in an intrinsic un-doped form. Thus diamond can be utilized as a heat spreading substrate for semiconductor components in a number of high power density applications. Furthermore, through the doping of the polycrystalline diamond, the heat spreader may also be conductive, thus enabling the heat spreader to become an electrical connection, if so desired. The advent of large area polycrystalline diamond produced by a chemical vapour deposition (CVD) technique has expanded the applications for diamond heat spreaders via an increase in area and a reduction in cost. Furthermore, the steadily increasing size of available single crystal synthetic diamond plates is also enabling use of such materials in heat spreading applications which require extremely high thermal performance.
Electronic device packages comprising integrated diamond heat spreaders are known in the art. For example, US2012/003794 discloses an electronic device package configuration in which a diamond thermal heat spreader is disposed between a carrier pad and an overlying semiconductor die. The composite carrier pad/diamond heat spreader/semiconductor die structure is then mounting within an opening of a lead frame. Wire bonds are formed between the semiconductor die and the lead frame and the whole structure is encapsulated in a mould material.
US2010/0149756 discloses an alternative arrangement for integrating a diamond heat spreader into an electronic device package. This document proposes that a diamond heat spreader is mounted to a metal frame and that this composite diamond heat spreader/metal frame structure is bonded over a ceramic carrier substrate on which a semiconductor die is mounted such that a surface of the diamond heat spreader is in contact with, but not adhered to, a surface of the semiconductor die. A heat sink is them mounted over the composite diamond heat spreader/metal frame structure such that a surface of the heat sink is in contact with, but not adhered to, a surface of the diamond heat spreader.
While the aforementioned configurations provide potentially viable solutions to the problem of integrating a diamond heat spreader into an electronic device package it is an aim of certain embodiments of the present invention to provide new configurations which can be made more compact in size, provide good heat spreading and/or heat sinking capability, and which are more suited for mounting into a range of different electronic device and/or heat sink configurations thereby providing a commercial product which can be used in a wider range of electronic device types, configurations, and applications.
For example, the present inventors have noted that the configuration described in US2012/003794 requires, as an essential feature, the presence of a carrier pad. In the described embodiments the carrier pad is mounted within an opening of a lead frame with a diamond heat spreader and a semiconductor die mounted on top of the carrier pad. The carrier pad thus acts as a supporting substrate for the heat spreader and semiconductor die. As the carrier pad is an integral part of the described electronic device package, it is not possible to readily change the material or construction of the carrier pad according to a particular electronic device application or configuration. Furthermore, the presence of the carrier pad increases the depth of the electronic device package and thus may not be usable in certain electronic device configurations which require very thin electronic device packages.
Similar problems may also apply to the configurations described in US2010/0149756. In the configurations described therein, the semiconductor dies are not directly mounted to the diamond heat spreader but rather are mounted to a separate ceramic substrate comprising metal connections disposed therein. A stacked structure is formed comprising ceramic support substrate/semiconductor die/heat spreader-metal holder complex/heat sink. This stacked structure based on a ceramic supporting substrate increases the depth of the electronic device package and thus may not be usable in certain electronic device configurations which require very thin electronic device packages. Furthermore, a heat sink having a shape complimentary to an upper recess in a diamond heat sink/metal frame composite structure appears to be required to mount the heat sink in contact with the diamond heat spreader. As such, the mounting configuration for the diamond heat spreader does not appear to be readily applicable to a generic heat sink having a substantially planer mounting surface.
FIGS. 1 to 3 illustrate several possible electronic device package configurations which aid in setting the context for the present invention. Like reference numerals have been used for like parts to aid comparison of the configurations illustrated in FIGS. 1 to 3.
FIG. 1 shows a schematic diagram illustrating a standard RF device configuration. The configuration comprises a semiconductor component 2 mounted on a metallic heat spreader 4 via a bonding material 6. An electrically insulating ceramic frame 8 is provided on the metallic heat spreader 4. Electrical connections 10 are mounted on the electrically insulating ceramic frame 8 and configured to electrically connect to the one or more semiconductor components via wire connections 12. The package is encapsulated with an encapsulating cap 14 and mounted on a metallic heat sink 16 via a bonding material 18. An insulating layer 20 is provided on the heat sink 16 to electrically insulate the electrical connections 10 from the heat sink.
FIG. 2 shows a schematic diagram illustrating an RF device configuration similar to that illustrated in FIG. 1 but incorporating a diamond heat spreader.
The configuration comprises a semiconductor component 2 mounted on a diamond heat spreader 3 via a bonding material 5. The diamond heat spreader 3 is mounted on a metallic heat spreader 4 via a bonding material 6. An electrically insulating ceramic frame 8 is provided on the metallic heat spreader 4. Electrical connections 10 are mounted on the electrically insulating ceramic frame 8 and configured to electrically connect to the one or more semiconductor components via wire connections 12. The package is encapsulated with an encapsulating cap 14 and mounted on a metallic heat sink 16 via a bonding material 18. An insulating layer 20 is provided on the heat sink 16 to electrically insulate the electrical connections 10 from the heat sink.
The configuration illustrated in FIG. 2 is therefore similar to that shown in FIG. 1 with the exception that a diamond heat spreader 3 is inserted between the semiconductor component 2 and the metallic heat spreader 4. The diamond heat spreader 3 aids in improving heat spreader immediately under the semiconductor component 2. However, in providing the diamond heat spreader 3 on top of the metallic heat spreader 4, the distance between the semiconductor component 2 and the heat sink 16 is increased. Furthermore, the number of interfaces between the semiconductor component 2 and the heat sink 16 is increased. Both these factors increase the resistance to heat flow from the semiconductor component 2 into the heat sink 16 and will counteract, to some extent, the beneficial effects of the diamond heat spreader 3.
FIG. 3 shows a schematic diagram illustrating an RF device configuration similar to that illustrated in FIG. 2 but incorporating the diamond heat spreader 3 into a window within the metallic heat spreader 4.
The configuration comprises a semiconductor component 2 mounted on a diamond heat spreader 3 via a bonding material 5. The diamond heat spreader 3 is mounted into a window within a metallic heat spreader 4 via a bonding material 6. An electrically insulating ceramic frame 8 is provided on the metallic heat spreader 4. Electrical connections 10 are mounted on the electrically insulating ceramic frame 8 and configured to electrically connect to the one or more semiconductor components via wire connections 12. The package is encapsulated with an encapsulating cap 14 and mounted on a metallic heat sink 16 via a bonding material 18. An insulating layer 20 is provided on the heat sink 16 to electrically insulate the electrical connections 10 from the heat sink.
The configuration illustrated in FIG. 3 is therefore similar to that shown in FIG. 2 with the exception that the diamond heat spreader 3 is mounted within a window in the metallic heat spreader 4 rather than on a top surface of the metallic heat spreader 4. The diamond heat spreader 3 aids in improving heat spreader immediately under the semiconductor component 2. Furthermore, by providing the diamond heat spreader 3 in a window within the metallic heat spreader 4, the distance between the semiconductor component 2 and the heat sink 16 is reduced relative to the arrangement shown in FIG. 2. Furthermore, the number of interfaces between the semiconductor component 2 and the heat sink 16 is reduced relative to the arrangement shown in FIG. 2. Both these factors reduce the resistance to heat flow from the semiconductor component 2 into the heat sink 16 and aid in increasing the beneficial effects of the diamond heat spreader 3.
An electronic device package configuration similar to that illustrated in FIG. 3 is described and illustrated in EP0932199. This document describes a package configuration in an electronic device is mounted on a diamond heat spreader which is itself mounted within a window of a copper clad molybdenum heat spreader or flange. An alumina frame is is provided on the copper clad molybdenum flange. Electrical connections in the form of copper leads are mounted on the alumina frame and configured to electrically connect to the electronic device via wire connections. The package is encapsulated with an encapsulating cap and mounted on a metallic heat sink 16 via a bonding material 18.
It is an aim of certain embodiments of the present invention to provide an improved electronic device package when compared to the aforementioned configurations.